Response to and signals of caloric restriction and intermittent feeding regimens

描述（由申请人提供）：在动物模型中，热量限制（CR）延长寿命并延缓疾病。由于两个主要原因，这一引人注目的观察结果很难转化为对人类健康的益处。首先，对大多数人来说，终生缺乏食物和减轻体重是不现实的；其次，在每次实验长达3年的啮齿类动物模型中，要确定对健康有益的潜在代谢和分子信号并不容易（以表明动物寿命更长）。我们最近应用了一种基于生物标志物的策略，使用高灵敏度、稳定的同位素质谱法测量体内代谢途径的通量作为结果测量，并寻找可能模仿CR的益处而不需要净负能量平衡的饮食方案，以解决这些局限性。我们的研究表明，间歇性喂养（IF）方案，如修改隔日禁食（mADF），在小鼠中再现了真正的CR的许多好处，而不会减轻体重或改变身体成分。对CR和某些mADF方案有反应的生物标志物包括整体细胞增殖（乳腺、前列腺、皮肤、肝脏、淋巴细胞）、脂肪组织动力学和脂肪分布、胰岛素敏感性和血管平滑肌细胞增殖。我们还观察到，在全身燃料利用和食物摄入的惊人循环方面，中饱能和CR方案之间存在相似之处，这表明CR本身就是中饱能的一种形式。在这个项目中，我们将使用快速反应的疾病风险生物标志物来探索潜在的更可行的饮食方案，并确定潜在的代谢和分子信号。具体目标是：1)建立再现CR效应所需的IF模式（禁食时间、摄食频率、常量营养素含量）。2)识别与有效IF方案相关的代谢信号（如NADH/NAD、糖原、脂肪酸氧化产物）。3)识别可能介导生物标志物变化的分子信号通路（如sirtuin通路基因表达和靶乙酰化、IGF-1/胰岛素轴、PGC-1、核因子）的变化，包括基因敲除小鼠（肝脏特异性SIRT3、IGF-1受体）的研究。4)评估运动或cr模拟药物与mADF的组合，以评估有益效果的放大。5)通过长寿研究和疾病模型（ApoE和ldl受体、饮食引起的肥胖/胰岛素抵抗和小鼠遗传癌症模型）的研究，确定基于生物标志物的结果测量是否能预测硬临床结果的影响。在所有的研究中，包括间歇性食物摄入的不同饮食干预将与经典的CR进行比较。中心假设是，摄入和代谢的周期性变化提供了启动保护程序的信号，而不需要改变体重。生物标志物的可用性允许以有效、迭代的方式识别饮食干预以及代谢和分子相关因素。总之，我们的目标是更好地理解IF和CR作用背后的代谢和分子信号，并将对生物标志物的影响与硬结局联系起来。公共卫生相关性：在动物模型中，热量限制延长寿命和延缓疾病的发现是显著的，但由于两个主要原因，很难转化为人类公共卫生的益处：首先，对大多数人来说，一辈子不吃东西、体重减轻是不现实的；其次，由于每次实验都需要3年或更长时间才能证明动物寿命更长，所以很容易识别出这些好处背后的潜在信号。我们已经确定并将在这里详细探讨饮食方案（间歇性禁食与随意摄入交替），这些方案可能不会导致体重减轻，而且对于人类的长期依从性来说可能更可行。我们发现，在我的实验室开发的灵敏、快速的转变测试可以作为有益的标记，这为梳理饮食影响背后的生化和分子信号提供了可能性，这样就可以开发出模仿这些影响的药物。

DESCRIPTION (provided by applicant): Caloric restriction (CR) extends life-span and delays diseases in animal models. This remarkable observation has been difficult to translate into human health benefits, for two primary reasons. First, a life-time of food deprivation and reduced body weight is not practical for most people; and, second, it has not been easy to identify the underlying metabolic and molecular signals responsible for health benefits in rodent models when each experiment takes up to 3 years (to show that animals live longer). We recently applied a biomarker- based strategy, using highly sensitive, stable isotope-mass spectrometric measurements of fluxes through metabolic pathways in vivo as outcome measures, and looked for dietary regimens that may mimic the benefits of CR without requiring net negative energy balance, to address these limitations. Our studies have shown that intermittent feeding (IF) regimens such as modifed alternate-day fasting (mADF) reproduce many of the benefits of true CR in mice, without weight loss or change in body composition. Biomarkers that respond to CR and certain mADF regimens include global cell proliferation (mammary, prostate, skin, liver, lymphocytes), adipose tissue dynamics and fat distribution, insulin sensitivity, and vascular smooth muscle cell proliferation. We also observed similarities between IF and CR regimens with regard to striking cyclicity of whole-body fuel utilization and food intake, indicating that CR is itself a form of IF. In this project, we will use rapidly responsive biomarkers of disease risk to explore potentially more feasible dietary regimens and to identify underlying metabolic and molecular signals responsible for benefits. Specific aims are, 1) establish the pattern of IF required to reproduce the effects of CR (duration of fasting, feeding frequency, macronutrient content). 2) Identify metabolic signals (e.g., NADH/NAD, glycogen, fatty acid oxidation products) associated with effective IF regimens. 3) Identify changes in molecular signaling pathways (e.g., sirtuin pathway gene expression and target acetylation, IGF-1/insulin axis, PGC-1, nuclear factors) potentially mediating changes in biomarkers, including studies in gene knock-out mice (liver-specific SIRT3, IGF-1 receptor). 4) Evaluate combinations of exercise or CR-mimetic drugs with mADF, to assess amplification of beneficial effects. 5) Determine whether biomarker-based outcome measures predict effects on hard clinical outcomes, through longevity studies and studies in disease models (ApoE k.o. and LDL-receptor k.o., dietary-induced obese/insulin resistance, and genetic cancer models in mice). In all studies, different dietary interventions involving intermittent food intake will be compared to classic CR. The central hypothesis is that cyclic changes in intake and metabolism provide signals that turn on a conservation program, without requiring changes in body weight. The availability of biomarkers allows identification of dietary interventions and of metabolic and molecular correlates in an efficient, iterative manner. In summary, our goal is to better understand the metabolic and molecular signals underlying the effects of IF and CR, and to correlate effects on biomarkers with hard outcomes. PUBLIC HEALTH RELEVANCE: The findings that caloric restriction extends lifespan and delays diseases in animal models are remarkable, but have been difficult to translate into human public health benefits for two main reasons: first, because a lifetime of food deprivation and reduced body weight is not practical for most people, and second, because it has been easy to identify the underlying signals responsible for these benefits, when each experiment takes 3 or more years to show that animals live longer. We have identified and will explore here in detail dietary regimens (intermittent fasting alternated with ad-libitum intake) which may not result in weight loss and are likely to be much more feasible for long-term compliance in humans. Our discovery that sensitive, rapid turn-around tests developed in my laboratory may be used as markers of benefit opens the possibility of teasing out the biochemical and molecular signals that underlie the effects of diet, so that drugs which mimic these effects might be developed.